The most pertinent prior art with respect to the present invention known to the inventors relates to subscription television systems in which communication of billing data to individual subscribers of the system is made possible. See U.S. Pat. No 4,487,217 to Block et al., which discloses a subscription television system in which all billing calculations are carried out at the decoder, that is, at the individual subscriber's location. When a subscriber makes a payment, e.g., by simply mailing a check to the broadcaster, the broadcaster then sends a message which is detected by that particular decoder and used by it to update the user's credit and/or account balance information The decoder then controls whether the user is to have access to a particular program or not in accordance with this billing information, and possibly also in accordance with other sorts of access controls transmitted by the broadcaster For example, each program transmitted may include an indication that it belongs to a particular "tier" or class of programs. The decoder then permits access to the program if programs of that tier had previously been authorized.
The Block et al patent also discloses that teletext data, that is, textual information relating to stock market reports and the like, could also be transmitted using this system. However, the teletext data discussed in the Block et al patent appears to be system-wide data, that is, data relevant to all subscribers of the system more or less equally. The Block et al. patent does not teach any way in which, for example, an individual broadcaster may send a chosen subscriber a personal message other than billing update data, as above.
"Specification of Standards for Broadcast Teletext Signals," a document published by the British Broadcasting Corporation et al. in September, 1976, describes the teletext broadcasting system in effect in the United Kingdom. According to this system, teletext information such as closed-captioned programming is available for the hearing impaired. According to this system, as understood by the applicants, the subscriber simply depresses a button on a key pad comprised by the decoder, and the decoder then selects alphanumeric data which is transmitted during the vertical blanking interval of the standard television signal. The decoder can then add this closed-captioned textual material directly to the video screen, so that it can be seen by the hearing impaired. Again, however, this material is transmitted system-wide, and there is no provision made for transmission of individual messages to individual subscribers.
In two co-pending applications assigned to the assignee of the present application Serial Nos. 883,301 filed July 8, 1986, and 883,310, filed July 8, 1986, there is described an improved subscription television system. According to the inventions described therein, individual teletext messages may be transmitted to individual subscribers. The manner in which this is done is described below. For purpose of understanding the present invention, it may be stated that the signal which is transmitted from the broadcaster includes messages which are directed to individual decoders. The decoders recognize that a message has been transmitted to them. They then subsequently select teletext information transmitted as part of the composite audio, video, teletext and data signal and display this to the individual subscriber. That system also includes transmission of system-wide control data, that is, data which is relevant to operation of all the decoders, such as identification of the video program being transmitted at any particular time.
One limitation on the communication system described in these applications is that individual decoders must be individually authorized by means of messages sent individually to them to receive certain information, specifically in order to receive teletext messages. While this is generally feasible, there is a limitation on the system throughput, as each decoder must be addressed individually.
The present invention recognizes that in some cases it may be desirable for an individual transmitter, for example, located at a corporate head office, to be provided with the capability to simultaneously transmit a single message, which might include video, audio, teletext or utility data to be transmitted, to a number of individual local offices. Preferably, the selection of the offices and of the information signal to be transmitted can be made individually at the transmitter location, either by corporate officials or by an intermediate service company. In this way significantly improved flexibility is provided.
For example, suppose a corporation occasionally wishes to send the identical message to all of its branch laboratories, research stations, service offices and sales offices. The message may comprise video, audio, teletext or utility data. [The distinction between teletext and data in this context is that "teletext" refers to textual information solely for display on a CRT or the like, whereas "utility data" refers to ordinary RS-232 data, i.e. to inter-computer communications]. At other times it may be desirable to send a directive only to the research facilities, at another time to the marketing groups, and so on.
In order to do so it is an object of the invention to provide a so called "commercial decoder" which is supplied to all locations with which such communications is desired. At the central location, that is, at the corporate headquarters in this example, a control device is provided to assign individual decoders to groups of decoders, and to define which services i.e., audio, video, teletext and/ or utility data - each group is to receive at any given time. Individual signals may be sent to each of the decoders identifying its present group assignment. Thereafter, an indication of the services which the decoders of each group are to decode and present to the users is transmitted regularly. In effect, the decoders themselves determine which services are to be decoded from the transmitted signal and made available to the users. In this way, simply by reconfiguring the groups and/or the "service package", the central transmitter can control which offices receive the various information signal portions of the transmitted "composite signal", all in a highly efficient, flexible, and orderly fashion.
There are a number of constraints on the design of the system. Briefly stated, it is an object of the invention to permit the following capabilities:
Because the cost of transponder time varies over the 24 hours of each day, it should be possible to transmit messages when desired, i.e. during the night, for example. This requires a means for remote actuation of a recording device.
The service should be controlled by the network user, that is by the corporate headquarters only, not by the decoder. In particular the network user expects that all the receivers will act in an identical way. This is in contrast to the subscription television use of the communications system of the invention, in which the individual subscriber selects particular programs
The revenue earned by the satellite owner should be derived only from a network user, not from the individual decoder users, in order to simplify bookkeeping and the like. By comparison, in the subscription television system, revenue is derived from each individual user.
It seems likely that some customers may be one time or very sporadic service users. It should be possible to allow new customers to be added readily, without affecting service to existing customers.
It should also be recognized that the decoder will typically remain chained to a single transponder for a relatively long periods of time, as opposed to the individual subscriber system, in which the user must be allowed to rapidly change channels, as one does with conventional television set. Therefore "lockup," that is, reception of the signal after channel change or power up, may be permitted to consume several seconds in the case of the commercial decoders.
As described above, the network user should be permitted to reclassify those of his decoders which receive given services at given times, i.e., to change their groups, and this should be readily alterable for convenience' sake.
Allocation of the services, whether by the network user or by an intermediate satellite service company, should be possible at a single central site. Furthermore, network planning and decoder group assignment should be permitted on the spot and be implemented by software, as opposed to repairing laborious hardware modifications, which would take advance planning and be more costly.
As indicated above, the prior art suggests that individual decoders can be addressed for transmission of billing information. It would also be desirable if individual user messages, this including video, audio, teletext and data, could be transmitted to individual users or groups of users so as to provide an additional communications facility not previously made available. If this is to be done, there are several criteria which must be met. Paramount among these is security; preservation of the secrecy of the message and its availability only to the particular addressee is of utmost importance.
It is therefore stated broadly to be an object of the invention to provide a communication format and system in which individual groups of decoders can be addressed in a convenient and readily alterable fashion, and in which particular classes of service can be allowed to each decoder in the group. More particularly, it is an object of the invention to provide a ready means for establishing, at a transmitter location, the identity of decoders in a particular group, and for transmitting at regular intervals an indication of the service to be made available to the decoders of each group, whereby ready reallocation of services is possible.
In assigning individual decoders to groups so as to thereafter be able to readily redefine the services allowed to each of the decoders, it is desirable that "historical" records of the group assignments for each of the decoders be maintained, such that plural "normal" assignments are available, and so that selection between several common arrangements is readily possible and does not involve excessive operator input. In order to do so, it is desirable that a "data base" be maintained concerning each of the individual decoders, whereby such updated records can be readily provided and changes can readily be made, and to do so is an object of the invention.
It is a further object of the invention to provide a communication system in which communication of audio, video, teletext and data to groups of decoders can be accomplished in an extremely secure and tamper-proof fashion.
It is a further object of the invention to provide a communications format and system in which individual text messages can be transmitted to individual subscribers, yet in which a network user at a transmitter location can send identical messages to groups of decoders, such that groups of decoders can receive a single text message transmitted simultaneously, while at the same time individual users can be addressed individually, using the same overall transmission format and transmitter hardware.
It is a further object of the invention to provide a system in which the network user can effectively control what is received by an individual decoder, and in which such control can be readily altered by an operator at the transmitter location without requiring any hardware modifications to any decoder or the equivalent.
It is a further object of the invention to provide the transmitter with the capability to activate a video cassette or other recorder at the decoder location, so that a message sent at night (to take advantage of lower transmission costs) can be recorded automatically and be available to be viewed when convenient.
The above needs of the art and objects of the invention are satisfied by the present invention, which comprises a communications format and system in which an operator at a central transmitter location assigns individual decoders in a system to groups. An "addressed packet" addressed to the individual decoder identifying its particular group assignment may be transmitted. Thereafter, on a regular basis, control signals indicating which services (i.e. audio, video, teletext and/or data) each group is permitted to decode are transmitted. Each of the decoders of the particular group is enabled to decode those particular services and no others.
More particularly, each decoder is provided with a "user address" and a "secret serial number". Each decoder is designated to be part of one or more particular groups by storing one or more group codes in its memory. There may be up to 255 unique group codes used by a network user. For example, a corporation may use the group codes in order to subdivide its operation, e.g. factory decoders are group 32, sales office decoders group 37, and so on. All decoders assigned to the same group will receive exactly the same service.
A "service" is defined as a particular portion of the composite audio, video, teletext and utility data signal used according to the preferred embodiment of the invention. As noted, the services may be video, utility data, audio, and/or teletext.
A "service package" is defined as a set of services. There may be up to some maximum number of service packages available at any one time. Typically, a service package is purchased by a customer of the network operator for use in distributing information to the groups. Two service packages may use the same service. For example, a French speaking sales group would receive the same video but different audio than would an English speaking sales group. Thus these two service packages would both include the same video service.
The composite signal includes a set of system-wide control information, or "system data", which is used by each decoder to control various system level operations. A portion of the "system data" is the so-called "commercial control sequence". This comprises a number of commands, each defining the current assignment of services to groups. Membership in a group is transmitted to the decoder by means of an individually addressed message which is transmitted only sporadically. By comparison, a portion of the commercial control sequence is transmitted once per "cryptocycle", that is, each time a complete set of the system data is transmitted.
All of the control data is preferably encrypted, and in general is transmitted a multiplicity of times for ensuring the accuracy of its decoding and for ensuring its security. Typically, each element of the system data, including each portion of the commercial control sequence, is transmitted in identical format five times in a row during each cryptocycle.
Transmission of teletext may involve several additional features For example, certain teletext information may be repeatedly transmitted by the transmitter, in order to provide certain frequently used information, referred to as "templates." The templates may be used by the decoder to complete a message in both the commercial decoder and the individual decoder embodiments of the invention. In either case, the decoder's microprocessor stores certain data which varies with respect to the individual decoder, and completes the message by inserting this "user-specific" data into the template provided by the transmitter.
In general, the commercial decoder is controlled completely from the transmitter, that is, no input device is provided to the decoder other than a simple on/off switch. Indeed, the message transmitted by the transmitter may also cause the decoder to output an external signal, e.g., to activate a video cassette recorder, to record a message sent from the head office of a corporate transmitter or the like. On the other hand, in some embodiments, user input may be desirable, e.g., to select templates or the like, and such is accordingly also within the scope of the invention.
The same composite communication signal format is used in the commercial decoder and in the individual subscriber embodiments of the invention. In each, the signal format includes transmission of a complete set of system data over a number of fields, sixteen in the preferred embodiment. Each field is transmitted as a number of lines, and contains a horizontal blanking interval portion, which includes the audio, a vertical blanking interval which includes system data, used to transmit data relevant to the operation of all the decoders in the system, addressed packet data used to send individual messages to individual decoders, and teletext if any, and a video portion, which in the preferred embodiment is encoded according to the so-called "B-MAC" format, which is discussed below. Both the system data and the addressed packets as mentioned above include key information which must be used by the decoder to decode the various encrypted portions of the signal. In this manner a very high degree of security is provided.
In the preferred embodiment, the system data is extensively protected by means of additional error correction characters and by duplication, such that it is very reliably received. Due to this duplication, the system data required for operation of the system cannot be transmitted in a single line of a single field. Therefore, the system data is divided into a number of groups for separate transmission in plural fields; in the preferred embodiment, this number is three. The system data transmitted in a given field is also duplicated and transmitted repetitively a predetermined number of times, five in a preferred embodiment, such that majority logic can readily be used to ensure correct receipt of the system data.
The system data includes in addition to the control data described above an encryption key which is used in the decoder to decrypt portions of the video, audio and teletext information. By virtue of the very high degree of security provided by the duplicative transmission and error correction facility, system data is received with high reliability. The key is changed at the completion of each "cryptocycle" that is, upon complete transmission of the system data, to further protect against its illegal duplication.
According to the present invention the commands making up the commercial control sequence are transmitted as part of the system data, so that these similarly are transmitted and received with a high degree of reliability. In the preferred embodiment, one command is transmitted per set of system data, so that transmission of the complete commercial command sequence extends over a number of cryptocycles. The received commands are stored by the decoders until the complete sequence has been received, indicated by transmission of a START command, at which time all commands are implemented.